Would installing a Y-valve with a hose to a strainer in the bilge (or some other low area to avoid drilling holes) along with the holding tank pump qualify?
Just for the purpose of the race, unless their specifications had more requirements, it wouldn't have to "be sanitary." Heck, neck the inch-and-a-half hose down to 1" and just put the end under the engine pan.
Wth regard to the structural grid system, one doesn't want to willy-nilly drill holes through it because there shouldn't be any holes in the high-stress areas. Several years go I had looked at a really nice boat but the owner or installer had drilled fairly large holes through the grid for his forced air heater ducts so that was a deal breaker. If it must be done I'd consult with the manufacturer, or if not available, a structural engineer (and get the results in writing if possible, but probably not possible).
